Thank you Salmonmac....What you said is correct:
"On the last row (I take this to be the knit row)...... "
Yes that was the problem with the directions which say:
"Continue until both pieces measure...

To answer your question, yes the purl row (the fourth row) is a cable row.
The pattern is from Cascade yarns, Cascade 128 Superwash Weskit vets designed by Betty Balcomb.
Actually I do not understand...